1. Field of the Invention
The present invention generally relates to on-vehicle information processors for providing map information based on map data and, more particularly, to an on-vehicle information processor in which a large volume of map data and associated map management data is managed efficiently.
2. Description of the Related Art
FIG. 10 is a block diagram showing a construction of an on-vehicle information processor disclosed in Japanese Laid-Open Patent Application No. 10-253367. Referring to FIG. 10, the on-vehicle information processor comprises applications 101-103 for providing services to a user by processing map data and the like; an operating system 104 for providing basic functions related to a recording medium 105 for storing map data and the like and a memory 106 for temporarily storing map data when the application is executed; a cache 111 for caching the map data and the like; and a device driver 121 for directly controlling the recording medium 105. The applications 101-103 and the operating system 104 are stored in, for example, a read-only memory (ROM) and executed by a microprocessor after being developed in a random access memory (RAM) or the like.
A description will now be given of the operation according to the related art.
FIG. 11 shows an example of how a cache is used in the related-art on-vehicle information processor.
When any of the applications 101-103 reads out the map data from the recording medium 105 via the operating system 104, the map data is stored in the cache 111 and retained therein according to a predetermined caching system. When the cache 111 becomes full, the data is discarded appropriately. When any of the applications 101-103 accesses the data stored in the cache 111, accessed data, for example, data items 111-1-111-3, are locked so that the other applications are prevented from accessing the data 111-1-111-3. In this way, the integrity of the cache 111 is maintained.
The applications 101-103 provide to the user based on the map data thus read out. For example, the application displays a road map on a display.
As described, in the related-art on-vehicle information processor, the data is locked so that applications other than the initially accessing application are prevented from accessing that data. Therefore, accessing from a plurality of applications the same data in the cache is not permitted. Accordingly, improvement in the processing speed cannot be hoped for.
Accordingly, a general object of the present invention is to provide an on-vehicle information processor in which the aforementioned drawback is eliminated.
Another and more specific object is to provide an on-vehicle information processor in which the processing speed is improved by allowing a plurality of applications to access the same map data temporarily stored in a map data cache.
Still another object of the present invention is to provide an on-vehicle information processor in which map data and map management data read out by a data reading unit are managed independently such that the map data and the map management data are read out from a data managing unit when required, so that the efficiency in processing an application is improved.
The aforementioned objects can be achieved by an on-vehicle information processor for providing map information based on map data, comprising: application processing means for providing predetermined map information based on map data and map management data; a data reading unit for reading the map data and the map management data from a recording medium; a data management unit for managing the map data and the map management data independently; and a request analyzing unit for responding to a request from the application processing means to permit access from the application processing means to the map data and the map management data managed by the data management unit.
The data management unit may acquire the map management data provided initially to the application means, so as to manage the acquired map management data; the request analyzing unit reads out the map management data from the recording medium via the data reading unit so as to supply the map management data thus read out to the application means, when the map management data is initially required by the application means; and the request analyzing unit may supply the map management data managed by the data management unit to the application means when the map management data is subsequently required by the application means.
The data management unit may be provided with a map data cache and a control unit for controlling the map data cache.
The control unit in the data management unit may control the total size of map data stored in the map data cache to be smaller than a predetermined upper limit.
The request analyzing unit may grant access from a plurality of application means to the same map data stored in the map data cache.
The map data cache may store count information indicating a number of application means accessing a storage area storing the map data, and the control unit may determine the map data stored in the map data cache that should be discarded, based on the count information stored in the map data cache.
The map data cache may store information relating to chronological sequence of storage of the map data or information indicating time of access to the map data, and the control unit may determine the map data stored in the map data cache that should be discarded, based on the information stored in the map data cache.